JPH02119117A - Positioning method and equipment for first and second objects - Google Patents

Abstract

PURPOSE:To enable highly accurate positioning of objects by a simple structure even in the case where the wavelength of exposure light and that of alignment light are different by interposing a projection lens between objects arrange so as to face each other, forming a first and a second marks on each of the objects, and arranging two diffraction points spaced at a specified interval on each of the marks. CONSTITUTION:Two mask marks 41-1, 41-2 composed of diffraction grating are formed as a mask 11 on a first object, and the marks 41-1, 41-2 are spaced at a specified interval 2r. A second mark as a wafer mark 42 composed of a diffraction grating is formed on a wafer 12 as a second object. From a point (a) of the mask 11, exposure light is focused on a wafer 12 via a projection lens 13; alignment light from a laser 43 is divided into two beams by mirrors 44-1, 44-2 as transferring means, transferred by the mark 41-1, 42-2, subjected to transmission diffraction by each of the mask marks, and two diffraction lights are realized, thereby enabling highly accurate positioning of objects.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for aligning first and second objects, such as aligning a mask and a wafer during a projection exposure process in semiconductor manufacturing. The present invention relates to a method and apparatus for combining.

[Prior Art] In the projection exposure process of semiconductor manufacturing, as shown in FIG. The image is reduced by the projection lens 3, projected onto the wafer 4, and transferred.

In order to accurately transfer the image of the circuit pattern onto the wafer, the mask and the mask need to be aligned before irradiation with exposure light. As a method for this alignment, there is a TTL method (Through The Lens), and one of these methods is described in the literature (G., Dubroeucq, 198
0゜ME, W. RTrutna, Jr., 1984.9
There is a method using two diffraction gratings, as disclosed in PIE).

In this method, as shown in FIG. 7, a diffraction grating 5.6 is formed on the mask 2 and the wafer 4, respectively.

The alignment light emitted from the laser 7 is diffracted along the path of the diffraction grating 6 of the wafer → the projection lens 3 → the diffraction grating 5 of the mask, and the diffracted light is detected by the detector 8 . Depending on the intensity of this diffracted light, the relative positions of the mask and wafer are adjusted so that they are aligned.

This alignment light uses light with a wavelength of 500 nm or more so that the resist on the wafer is not exposed. Currently, the most common wavelength is 633 n
A II e - N e laser beam of s is used.

By the way, as the degree of integration of semiconductors is currently increasing,
There is a tendency for the line width of circuit patterns to become thinner. That is, the resolution R (-λ/NA, λ: wavelength of exposure light) tends to be reduced. Therefore, the wavelength λ of exposure light is becoming shorter. Currently, exposure light uses g-11ne (43
8rv) light is used, but in the future, exposure light waves,
It is planned that the length will be further shortened and a +-11ne (385 nm) or KrF excimer laser (248 tv) will be used.

Therefore, even now, the wavelength of exposure light and the wavelength of alignment light are different, but in the future, i-1-11ne (3
When a 65n or KrF excimer laser (248 nm) is used as exposure light, it is expected that the difference in wavelength between the two will become even larger. In such cases, as will be explained below, it has become difficult to align the mask and the wafer due to the presence of significant chromatic aberration in the projection lens with respect to the alignment light.

[Problems to be Solved by the Invention] The distance between the mask and the wafer is set such that exposure light emitted from the mask is converged by a projection lens and focused on the wafer. That is, the aberration of the projection lens is set to be minimum only for the exposure light, and the projection lens has chromatic aberration for light other than the wavelength of the exposure light (for example, alignment light).

As a result, when the exposure light is g-11ne (436rv) and the alignment light is a laser beam with a wavelength of 633 ns, the alignment light diffracted by the diffraction grating 6 of the wafer is as shown in FIG. , distance d(-
Focus on a position several tens of times away.

Conventionally, it has been believed that if the alignment light does not focus on the mask mark 5, the sensitivity of the detected diffracted light will deteriorate and alignment will not be performed accurately. Therefore, conventionally, as shown in FIG. 7, a folding mirror 9 is provided to correct the optical path length of the alignment light. Thereby, the alignment light is focused on the mask mark 5.

However, the exposure light is I-I 1ne(:(85nm
) or KrP excimer laser (248 nm), and when the wavelengths of the exposure light and alignment light are significantly different, such as when the alignment light is a laser light with a wavelength of 633 rv, a projection lens is used for the alignment light. There is significant chromatic aberration, and the alignment light is focused at a distance HD (-several thousand square meters) away from the mask 2, as shown by the two-dot chain line in FIG. In this case, even if an attempt is made to correct the optical path of the alignment light using a folding mirror, the structure of the folding mirror becomes large and complicated, making it almost impossible to correct the optical path of the alignment light.

Therefore, if the wavelengths of the exposure light and the alignment light are significantly different, the alignment light cannot be focused on the mask mark 5 because there is significant chromatic aberration in the projection lens with respect to the alignment light, and the mask and wafer cannot be focused. 1 could not be aligned.

An object of the present invention is to provide a simple structure even when the wavelengths of exposure light and alignment light are significantly different.
An object of the present invention is to provide a method and apparatus for aligning a mask (first object) and Ueno X (second object) with high precision.

[Means for Achieving the Object] In the alignment method of the present invention, first and second objects are arranged facing each other, and a projection lens is interposed between these first and second objects. first and second marks are formed on the first and second objects, respectively, each mark having two diffraction points spaced apart from each other by a predetermined distance; A method for aligning an object, in which alignment light emitted from a light source is irradiated to two diffraction points of a first mark and diffracted, and as a result, each of the two diffraction points of the first mark, A step of causing two predetermined orders of diffracted light to appear, and a step of exposing these two predetermined orders of diffracted light to a second one through a projection lens.
a step of transferring and diffracting light to two diffraction points of the second mark, and as a result, causing re-diffracted light of two predetermined orders to appear, respectively, from the two diffraction points of the second mark; A step of causing the re-diffracted lights of different orders to interfere with each other to form interference light; a step of detecting this interference light and, as a result, a step of emitting a detection signal having positional deviation information of the first and second objects; and this detection signal. adjusting the relative positions of the first and second objects based on the first and second objects to align the first and second objects.

[Operation] In the present invention, two diffracted lights emerge from two diffraction points separated from each other on the first mark, and these two diffracted lights are incident on two diffraction points separated from each other on the second mark. Then, two re-diffracted lights emerge from these two diffraction points, and these two re-diffracted lights are made into interference light, which is detected and aligned.

That is, in this invention, two diffracted lights of the first mark are incident on two diffraction points of the second mark, and further,
For detection, the two re-diffracted beams of the second mark are made into interference beams. Because of this configuration, unlike conventional
There is no need for the two diffracted lights of the first mark to be focused onto the second mark. Therefore, chromatic aberration may exist in the projection lens with respect to the alignment light. That is,
The alignment light and the exposure light may have different wavelengths. Therefore, even if the wavelengths of the exposure light and the alignment light are significantly different, the first object and the second object can be aligned with high precision.

[Example] Referring to FIGS. 1 and 2, a positioning apparatus according to a first example of the present invention will be described.

Two mask marks (first mark) consisting of diffraction gratings
41-1.41-2 is the mask (reticle, first object)
11. These two mask marks 41-
1.41-2 are spaced apart by a predetermined interval (2r).

On the other hand, one wafer mark (second mark) 42 made of a diffraction grating is formed on the wafer (second object).

This wafer mark does not need to be formed from one diffraction grating, but only needs to have two diffraction points that are spaced apart from each other and can diffract light. Note that the mask and wafer mark may be one-dimensional, two-dimensional, or checkered diffraction grating.

In the first embodiment, the exposure light (first virtual light) is 1-11
ne (365 ns) or KrP excimer laser (248 ns)
ns), and the alignment light is a laser beam with a wavelength of 633nm. As shown in FIG.
1 and the wafer 12 is set so that there is no aberration in the projection lens 13 with respect to the exposure light (first virtual light). That is, the exposure light (first virtual light) is
As shown by the broken line in the figure, the light is emitted from point a of the mask 11 and focused onto the wafer 12 via the projection lens 13 . However, chromatic aberration exists with respect to light (alignment light) having a wavelength other than the exposure light.

Here, as shown by two-dot chain lines in FIG. 2, two second virtual lights having the same wavelength as the alignment light are assumed. In this case, since this second virtual light has chromatic aberration with respect to the projection lens, it has the following optical path.

In consideration of the chromatic aberration with respect to the two second virtual lights, a virtual mask 11 is placed at a position spaced apart from the mask 11 by a distance d1.
-1 is placed, this virtual mask 11-
1 is assumed to be the first virtual point, and furthermore, a point separated by a distance d2 from the weno 112 is assumed to be the second virtual point C.
Assume that Then, the two second virtual lights are transferred to the virtual mask 11-1, as shown by the two-dot chain line in FIG.
ejects from the first virtual point of and passes through the mask 11,
It has an optical path that is converged by the projection lens 13, passes through the wafer 12, and as a result focuses on the second virtual point C.

In this first embodiment, as shown in FIG. 2, the mask marks 41-1 and 41-2 and the wafer mark 42 are located on the optical paths of the two second virtual lights. Furthermore, as shown in FIG. 1, the optical paths of the two ±1st order diffracted lights emerging from the two mask marks are
The optical path of the virtual light is matched. As a result, the two ±1st-order diffraction lights are shifted to two diffraction points on the wafer mark spaced apart from each other, as if they were focused on the second virtual point C.

Therefore, in this first embodiment, the mask and wafer are aligned as follows.

That is, the alignment light emitted from the laser 43 is converted into two light beams by the mirror 44-1 and the prism 44-2, and then transferred to the mask marks 41-1 and 41-2. As a result, the two light beams are each transmitted through and diffracted by the mask mark, resulting in two n-order (n=0.±1...
・) diffracted light appears.

At this time, the angle of incidence of the alignment light on the mask mark is set so that two ±1st-order diffracted lights among the n-order diffracted lights migrate along the optical paths of the two second virtual lights. There is. This angle of incidence is set by adjusting the angles of the mirror 44-1 and the prism 44-2.

The two ±1st-order diffracted lights that have migrated along the optical path of the second virtual light are transmitted to the wafer mark 42 via the projection lens 13 . The two ±1st-order diffracted lights are each reflected and diffracted at two diffraction points of the wafer mark 42, and two n-th order re-diffracted lights appear.

In this way, in this first embodiment, two
The two ±1st-order diffracted lights are not focused on the mark, but are incident on the two diffraction points on the wafer mark, and are
Two re-diffracted lights appear. Therefore, these two
In order to detect two re-diffracted lights, a step of interfering the two re-diffracted lights is required.

Therefore, two ±1st-order re-diffracted lights out of the two n-th-order re-diffracted lights are transmitted to the mirror 45, the lens 46, and the mirror 53.
-1, the light is transferred to a prism 53-2, and is caused to interfere with the prism 53-2 to become interference light. This interference light is incident on the detector 47. These two ±
The first-order re-diffracted light has positional information between the mask and the wafer based on the phase change. Therefore, the interference light has position information of the mask and the wafer. As a result, the detector detects a change in the intensity of the interference light, thereby emitting a detection signal having information on the relative displacement between the mask and the wafer.

This detection signal is processed by the signal processing device 48,
Based on the signal from the signal processing device 48, the position of the mask or wafer is adjusted by the position adjustment device 49.

As described above, in this first embodiment, the two ±1st-order diffracted lights of the mask mark are emitted from the first virtual point and are transferred as if they were focused on the second virtual point C. As a result, two ±1st-order diffracted lights are incident on two diffraction points of the wafer mark that are spaced apart from each other. Further, for detection, the two ±1st-order re-diffracted lights are made into interference lights. Due to this configuration, the two ±1 of the mask mark
There is no need for the next diffracted light to be focused onto the wafer mark. Therefore, chromatic aberration may exist in the projection lens with respect to the alignment light. That is, the alignment light and the exposure light may have different wavelengths. Therefore, even when the wavelengths of the exposure light and the alignment light are significantly different, the mask and the wafer can be aligned with high precision.

Furthermore, in the first embodiment, it is not necessary that two marks be formed on the mask, and even one mark may have at least two diffraction points formed thereon. Furthermore, it is sufficient that two diffraction points are formed on the wafer, and two diffraction grating marks may be formed on the wafer.

Furthermore, in this invention, the exposure light is g-11ne (436n
Of course, the present invention can also be applied to cases where the wavelengths of the exposure light and the alignment light differ only slightly, as in the case of light s). In this case, unlike the conventional case, since a folding mirror is not required, the structure is simple.

Next, a second embodiment of the invention will be described with reference to FIG.

In this embodiment, the alignment light passes through the lens 61 and the condenser lens 62 to the mask mark 41-1.41.
-2. At this time, the alignment light is incident on the mask mark (indicated by a broken line) toward the center of the entrance pupil of the projection lens 13. Mask mark 41-1
．． The two ±1st-order diffracted lights 41-2 pass through the entrance pupil and are irradiated onto the wafer mark 42, as shown by the solid line.

As described above, the wafer mark 42 may be a one-dimensional diffraction grating (FIG. 5A), a two-dimensional diffraction grating (FIG. 5B), or a checkered diffraction grating (FIG. 5C). . For these selections, the best method may be adopted depending on the usage conditions of the projection exposure apparatus. For example, during transfer of a circuit pattern, the mask and the wafer 1 may be aligned using alignment light. In such cases, either a two-dimensional diffraction grating (FIG. 5B) or a checkered diffraction grating (FIG. 5C) is used for the wafer mark. Thereby, the re-diffracted light of the wafer mark is distributed two-dimensionally. It is possible for a predetermined order of re-diffracted light of the two-dimensional re-diffracted light to be located outside the optical path of the exposure light. Therefore, if the mirror 45 is arranged so that this re-diffracted light of a predetermined order is detected, the mirror 45
does not block the exposure light.

Furthermore, whether the wafer mark 42 is illuminated with exposure light and the wafer mark resist is peeled off, or whether the wafer mark 42 is not illuminated with exposure light and the wafer mark resist is left as an afterimage is the user's next choice. Due to. That is, the user places the mask 1 at a position conjugate to the wafer mark 42.
Whether the wafer mark should be removed or left can be selected by forming a chromium-free window at point e on point 1 or by attaching chromium to point e to block exposure light.

FIG. 4 shows a modification of the detection means and signal processing means.

In FIG. 4, the mask 11 has mask marks 41-
As a mask mark 41-2, four marks A, B, C, and D are consecutively arranged, and as a mask mark 41-2, four marks a, b, c, and d are consecutively arranged. Note that these marks A to D, a to d may be placed on the dicing line outside the circuit pattern. Four marks A and B.

C and D are separated by a predetermined distance from four marks a, b, c, and d, respectively. On the other hand, there are four marks Aa, Bb, Cc on the wafer mark 42 on the wafer 112.
, Dd are arranged consecutively.

Therefore, when mark A and mark a on the mask are irradiated with alignment light, the diffracted light from these marks is transferred to mark Aa on the wafer and diffracted. In addition, when the alignment light is irradiated to the mark B... and the mark b..., the diffracted light is transferred to the mark Bb... of the Ueno 1. These marks A a - D on sea urchin/%
There is no problem even if d is the same continuous mark without being separated from each other.

There are the following two methods of signal processing using the above-mentioned marks.

A first method is to use a phase shift mechanism 52 illustrated in FIG. That is, this is a method in which the frequencies of the two incident beams are shifted by ω, and the mask 11 is irradiated. The signal output detected by this method is detected as a beat signal corresponding to the frequency difference ω. From this, the relative displacement between the mask 11 and the wafer 12 can be understood as a phase displacement (this is an application of the so-called heterodyne method).

As a second method, the pitch of marks Aa on the wafer is shifted by 1/4 pitch from the pitch of marks Bb.

Therefore, the diffraction angle of the re-diffracted light from the mark Aa and the diffraction angle of the re-diffracted light from the mark Bb are different. Therefore, the two re-diffracted lights are detected independently. 2
The difference between the two re-diffracted lights is calculated, and the mask and wafer are aligned so that this difference becomes zero.

When semiconductor devices are manufactured, for one wafer,
A plurality of circuit patterns are sequentially transferred.

Therefore, it is necessary to align the mask and the wafer each time transfer is performed. Therefore, a large number of alignment marks must be formed on the wafer.

For example, as shown in FIG. 4, marks Aa and Bb on the wafer are used for alignment when transferring the first layer, and marks Cc on the wafer are used when transferring the second layer. and mark Dd are used for alignment. However, when transferring the first layer, it is assumed that alignment light is irradiated to mark A and mark a of the mask, and alignment light is irradiated to mark B and mark b of the mask. In this case, the ±1st order diffracted light of each mark A, a, B, b is
It is transferred to mark Aa and mark Bb on the wafer. However, there is a possibility that the zero-order diffracted light of the marks A, a, B, and b is transferred to the mark Cc or mark Dd on the wafer.

In this case, the 0th order diffracted light is the mark Cc or the mark Dd
, and enters the detector 47, resulting in an error in positioning. In order to prevent such errors from occurring, as shown in FIG. It is sufficient if the interval 2 is set relatively large.

Furthermore, in the embodiment described above, a mirror is disposed between the mask and the wafer to guide re-diffracted light from the wafer mark to the detector. However, a mirror may be arranged so that the re-diffracted light of the wafer mark is guided to the detector after being transferred above the mask. Furthermore, two wafer marks may be arranged on the wafer and one mask mark may be arranged on the mask. Furthermore, as shown in FIG. 3, the two mask marks may be composed of one relatively long extended diffraction grating.

[Effects of the Invention] As described above, even when the wavelengths of the exposure light and the alignment light are significantly different, the first and second objects can be aligned with high precision with a simple structure.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an alignment device based on the first embodiment of the present invention, FIG. 2 is a schematic diagram for explaining the principle of the alignment device of FIG. 1, and FIG. , FIG. 4 is a plan view of a mask and a wafer showing a modification of the alignment mark arrangement, and FIG. 5A is a one-dimensional diffraction grating. FIG. 5B is a plan view of a two-dimensional diffraction grating, FIG. 5C is a plan view of a checkered diffraction grating, FIG. 6 is a schematic diagram of a conventional projection exposure apparatus, and FIG. 7 is a plan view of a conventional projection exposure apparatus. It is a schematic diagram of the alignment device. 11...Mask (first object), 12... Wafer (
second object), 13...projection lens, 41-1°41
-2...Mask mark (two [1l of the first mark)
lil refraction point) 42...Wafer mark (two diffraction points of the second mark) 43...Laser (light source), 44
-1... Mirror (transfer means), 44-2... Prism (transfer means), 47... Detection 8 (detection means), 4
9...Position adjustment device (position adjustment means), 53-2.
... Prism (interference means). Applicant's Representative Patent Attorney Takehiko Suzue Figure A Figure B Figure C Figure Figure C

Claims (1)

[Claims] 1. A first and a second object are arranged opposite to each other, a projection lens is interposed between the first and second objects, and the first and second objects A method for aligning first and second objects, wherein first and second marks are respectively formed on the object, and each mark has two diffraction points spaced apart from each other by a predetermined distance. , the alignment light emitted from the light source to the first mark 2
a step of irradiating and diffracting two diffraction points on the first mark, and as a result, two predetermined orders of diffracted light appear from each of the two diffraction points of the first mark; , respectively, are transferred to the two diffraction points of the second mark through the projection lens and diffracted, so that the two diffraction points of the second mark
A step of causing two re-diffracted lights of predetermined orders to appear from each of the two diffraction points, a step of making these two re-diffracted lights of predetermined orders interfere with each other to form interference light, and detecting the interference light. As a result, a step of emitting a detection signal having positional deviation information of the first and second objects, and adjusting the relative positions of the first and second objects based on the detection signals, A method for aligning first and second objects, comprising: aligning the objects. 2. It is assumed that the first virtual light is emitted from the first object (11), and the distance between the first and second objects (11, 12) is such that the first virtual light is emitted from the first object. A first virtual point (b) is set to be emitted and converged by a projection lens to be focused on a second object, and is located at a predetermined distance from the first object (11) on the opposite side of the projection lens. ) is assumed, and a second virtual point (c) located at a predetermined distance from the second object (12) on the opposite side of the projection lens is assumed, and has a wavelength longer than the wavelength of the first virtual light. It is assumed that two second virtual rays are emitted from the first virtual point (b), and these two second virtual rays are emitted from the first virtual point (b), and each , has an optical path that passes through two diffraction points of the first mark, is converged by a projection lens, passes through two diffraction points of the second mark, and is focused on a second virtual point (c). , so that the two diffracted lights of predetermined orders emerging from the two diffraction points of the first mark are transferred along the optical paths of the two second virtual lights to the two diffraction points of the second mark. 2. The method for aligning first and second objects according to claim 1, wherein the first mark is irradiated with alignment light. 3. The first object according to claim 2, wherein the first object is a mask in a projection exposure apparatus, the second object is a wafer, and the first virtual light is exposure light. and a method for aligning a second object. 4. The method of aligning the first and second objects according to claim 1, wherein the alignment light is uniformly irradiated over a wide range to the first mark of the first object. 5. The first and second marks according to claim 1, wherein the alignment light is selectively irradiated to two diffraction points of the first mark.
How to align objects. 6. The first and second marks according to claim 1, wherein the first mark includes a plurality of sets of two marks each having a diffraction point.
How to align objects. 7. The first mark is a one-dimensional diffraction grating, a two-dimensional diffraction grating, or a checkered diffraction grating, and the second mark is a one-dimensional diffraction grating, a two-dimensional diffraction grating, or a checkered diffraction grating. 7. A method for aligning first and second objects according to any one of claims 1 to 6, wherein each diffraction grating includes two diffraction points. 8. The first mark includes a plurality of marks arranged on the dicing line outside the circuit pattern of the mask and each having two diffraction points, and these marks are arranged on the dicing line outside the circuit pattern of the mask, and these marks 8. The method of aligning the first and second objects according to claim 3, wherein the first and second objects are arranged symmetrically with respect to a conjugate position with respect to the light. 9. The alignment light irradiation step includes a step of irradiating two alignment light beams with different frequencies, and the interference light detection step includes a step of detecting the interference light and emitting a detection signal as a beat signal. A method for aligning first and second objects according to any one of claims 1 to 8. 10. The method for aligning the first and second objects according to any one of claims 1 to 9, wherein the alignment light is a spherical wave that is incident on the entrance pupil of the projection lens. 11. The method for aligning the first and second objects according to any one of claims 1 to 10, wherein the two re-diffracted lights of predetermined orders are once made parallel and then made to interfere. 12. Claim 1, wherein the two predetermined order diffracted lights appearing at the two diffraction points of the first mark are ±1st order diffracted lights.
12. The method for aligning first and second objects according to any one of items 11 to 11. 13. In order to prevent the two 0th order diffracted lights appearing at the two diffraction points of the first mark from entering the second mark after passing through the projection lens, these 0th order diffracted lights are of the first and second objects according to any one of claims 1 to 12, wherein the angle of incidence on the mark and the interval between the two diffraction points of the first mark are set. Alignment method. 14. According to any one of claims 1 to 13, the two re-diffracted lights of the two predetermined orders appearing at the two diffraction points of the second mark are diffracted lights of the ±1st order. 1st and 2nd
How to align objects. 15. the first and second objects are arranged opposite to each other;
A projection lens is interposed between the first and second objects, and first and second marks are formed on the first and second objects, respectively, and each mark is spaced apart from each other by a predetermined distance. A first and second object alignment device having two diffraction points arranged, the device emitting alignment light and irradiating the two diffraction points of the first mark with the alignment light; as a result,
A light source that emits two predetermined orders of diffracted light from two diffraction points of the first mark; a transition means for transferring and diffracting light to two diffraction points, so that re-diffracted light of two predetermined orders appears from the two diffraction points of the second mark, respectively; an interfering means for causing the re-diffracted lights to interfere with each other to produce interference light; a detection means for detecting the interference light and emitting a detection signal having positional deviation information of the first and second objects; and based on the detection signal. a position adjustment device for aligning the first and second objects by adjusting the relative positions of the first and second objects. 16. It is assumed that the first virtual light is emitted from the first object (11), and the distance between the first and second objects (11, 12) is such that the first virtual light is emitted from the first object. A first virtual point (b) is set to be emitted and converged by a projection lens to be focused on a second object, and is located at a predetermined distance from the first object (11) on the opposite side of the projection lens. ) is assumed, and a second virtual point (c) located at a predetermined distance from the second object (12) on the opposite side of the projection lens is assumed, and has a wavelength longer than the wavelength of the first virtual light. It is assumed that two second virtual rays are emitted from the first virtual point (b), and these two second virtual rays are emitted from the first virtual point (b), and each , has an optical path that passes through two diffraction points of the first mark, is converged by a projection lens, passes through two diffraction points of the second mark, and is focused on a second virtual point (c). , so that the two diffracted lights of predetermined orders emerging from the two diffraction points of the first mark are transferred along the optical paths of the two second virtual lights to the two diffraction points of the second mark. 16. The apparatus for aligning first and second objects according to claim 15, wherein the first mark is irradiated with alignment light. 17. The first object according to claim 16, wherein the first object is a mask in a projection exposure apparatus, the second object is a wafer, and the first virtual light is exposure light. and a second object alignment device. 18. The apparatus for aligning the first and second objects according to claim 15, wherein the alignment light is uniformly irradiated over a wide range to the first mark of the first object. 19. The apparatus for aligning the first and second objects according to claim 15, wherein the alignment light is selectively irradiated to two diffraction points of the first mark. 20. The first and second object alignment apparatus according to claim 15, wherein the first mark includes a plurality of sets of two marks each having a diffraction point. 21. The first mark is one of a one-dimensional diffraction grating, a two-dimensional diffraction grating, and a checkered diffraction grating, and the second mark is one of a one-dimensional diffraction grating, a two-dimensional diffraction grating, and a checkered diffraction grating. 21. A device for aligning first and second objects according to any one of claims 15 to 20, wherein each diffraction grating includes two diffraction points. 22. The first mark includes a plurality of marks arranged on the dicing line outside the circuit pattern of the mask and each having two diffraction points, and these plural marks are arranged on the dicing line outside the circuit pattern of the mask, and these marks are 22. A device for aligning first and second objects according to any one of claims 17 to 21, wherein the first and second objects are arranged symmetrically with respect to a conjugate position with respect to the light. 23. Means for irradiating two alignment light beams having mutually different frequencies is provided, and the interference light detection means has means for detecting the interference light and emitting a detection signal as a beat signal. Claim 15. 23. The apparatus for aligning first and second objects according to any one of items 22 to 22. 24. The apparatus for aligning the first and second objects according to any one of claims 15 to 23, wherein the alignment light is a spherical wave incident on the entrance pupil of the projection lens. 25. The apparatus for aligning the first and second objects according to any one of claims 15 to 24, further comprising means for making two re-diffracted lights of predetermined orders parallel and then interfering with each other. . 26. The first and second diffracted lights according to any one of claims 15 to 25, wherein the two predetermined orders of diffracted light appearing at the first mark are ±1st order diffracted lights. Object alignment device. 27. These zero-order diffracted lights enter the second mark so that the two zero-order diffracted lights appearing at the first mark do not enter the second mark after passing through the projection lens. 27. Alignment device for first and second objects according to any one of claims 15 to 26, wherein the angle and the spacing between the two diffraction points of the first mark are set. 28. The first and second re-diffracted lights according to any one of claims 15 to 27, wherein the two predetermined orders of re-diffracted light that appear at the second mark are ±1st-order diffracted lights. object alignment device.